Films or sheets of linear polyester have been commercially available for many years. The film has excellent draw orientation and has proved to be especially well suited for the biaxial film orientation process resulting in films of outstanding properties. The film is also known as polyethylene terephthalate or PET and is strong and has excellent inherent chemical and thermal stability properties. The polymer preparation and film manufacturing processes are well known to those skilled in the art and are recited in many texts, including the Encyclopedia of Polymer Science and Engineering, second edition, volume 12, by John Wiley and Sons, Inc., pages 1 through 313; and numerous U.S. and foreign patents.
The myriad uses of polyester film have resulted in the need for modification of the basic film to provide special properties such as improved heat sealability and improved printability properties.
The present invention relates to an all polyester composite film structure that has superior physical properties. More specifically, the composite film structure of the present invention is composed of multiple polyester film layers which have improved properties when printed or embossed. The composite structure is particularly useful for the manufacture of credit or identification cards.
Identification and credit cards are made of multiple sheets of several polymeric materials, such as alternative sheets of polyester and interspaced sheets of paper or polyethylene. Such cards are in wide use throughout the world, but they possess several disadvantages. Firstly, the excess polymeric materials in the card manufacturing process are costly to recycle because they are not composed of one type of polymeric material. Secondly, the raised numbers and letters on the top surface of the cards tend to not print clear copies of the number and letters after repeated use in the machines that are used to make imprints of the credit card for preparing charge receipts.